1. GROUND-LEVEL EVENT (GLE)
SOLAR COSMIC RAY
GROUND-LEVEL EVENT (GLE)
ANISOTROPY
D. F. SMART and M. A. SHEA
AFRL (Retired)
SSSRC, NASHUA, NH, USA

2. The interplanetary
magnetic field
controls charged
particle propagation
between the Sun
and the Earth
An idealized
concept is the
Archimedes spiral
curve in the IMF
topology.
The IMF is actually
turbulent, with
magnetic scattering
centers.

3. The average mean free path in the IMF is the order of 0.1 AU.
With order of magnitude variations.

5. The spinning satellite method for anisotropy.
Sectored proton flux anisotropy (A) at ~30 MeV
The distance from the center indicates the
magnitude and direction of the particle flux.
The “B” line indicates the IMF direction
The center line is the Sun-Earth line.

6. Solar Particle Anisotropy
A directional dependence solar particle flux.
Solar particle anisotropy is radial distance and time dependent
Many definitions Maximum Minimum
THEORY
2 π Forward / 2 π Reverse Large
Forward Sector / Reverse Sector Large
Forward Steradian / 4 π Steradian Large

7. The spinning satellite method for anisotropy.
Particle flux anisotropy is a transient phenomena;
a duration of a few hours is typical.
Multiple sensors on a stabilized satellite can
also be used to measure particle anisotropy.

9. SOLAR COSMIC RAY EVENTS
THE LARGEST OBSERVED
SOLAR COSMIC RAY EVENTS
LARGEST GLE
4580 % (15-min data)
Flare at 23 N, 80W
2nd LARGEST GLE
2150 % (5-min data)
Flare at 14 N, 61 W
4th LARGEST GLE
373 % (5-min data)
Flare at 105 W

10. Cosmic ray trajectories have curved paths in the Earth’s magnetic field.
Cosmic ray stations view interplanetary space through allowed trajectories.
This leads to the concept of the asymptotic cone of acceptance.
Low and mid latitude stations have wide asymptotic cones of acceptance.
Polar stations have narrow asymptotic cones of acceptance.
As a result, polar stations view a narrow region of interplanetary space.

11. Cosmic ray trajectories have curved paths in the Earth’s magnetic field.
Cosmic ray stations view interplanetary space through allowed trajectories.
This leads to the concept of the asymptotic cone of acceptance.
Low and mid latitude stations have wide asymptotic cones of acceptance.
Polar stations have narrow asymptotic cones of acceptance.
As a result, polar stations view a narrow region of interplanetary space.

14. GLE 67
Flare 56
Bx +1.7, By +0.9, Bz -5.0
IMF Lat -69, Lon 333
P View Lat +68, Lon -28
GLE Start
GLE Max
Ft %
Ft. Smith 2 GV Asy Lon 266 Greenwich 84

15.
GLE 69

20. the anisotropy decreases, and the flux distribution becomes wider.
0o Pitch angle is along the IMF direction; 90o is perpendicular to the IMF direction.
During the initial phase of a highly anisotropic GLE, only those stations oriented so that they view the "forward “propagating solar particle flux will have a response.
As the event progresses the pitch angle distribution will undergo more scattering,
the anisotropy decreases, and the flux distribution becomes wider.

21. 180o is backscatter toward the sun
0o Pitch angle is along the IMF direction; 90o is perpendicular to the IMF direction.
180o is backscatter toward the sun
As the event progresses the pitch angle distribution will undergo more scattering,
the anisotropy decreases, and the flux distribution becomes wider.

22. Apatity
Oulu

23. APATITY
OULU

26. The possibility of pitch angle snapshots using AMS02 data.
AMS02 determines the rigidity and direction of each particle observed.
rigidity is momentum per unit charge.
At each high-latitude pass, they can record the GLE particles allowed.
Using a magnetic field model, the trajectory can be "traced back" to
establish the particle vector direction at the magnetopause boundary.
If they have the IMF vector direction (at Earth)
the "dot product" of these two vectors is the pitch angle.

27. Extreme anisotropy is a transient phenomena.
Time duration of hours or less
There will be a small persistent anisotropy as long as new fluxes
are being injected into the IMF field lines.

28. SUMMARY Extreme anisotropy is a transient phenomena.
Extreme anisotropy is a transient phenomena.
Time duration of hours or less
It is difficult to predict the degree of anisotropy to be expected.
General Characteristics:
GLE's from "well connected" western hemisphere active regions
normally have large initial anisotropies.
GLE's from central meridian active regions
normally have medium anisotropies.
GLE's from eastern hemisphere active regions
normally have low anisotropies.
There will be a small persistent anisotropy as long as new fluxes
are being injected into the IMF field lines.

30. SOLAR COSMIC RAY EVENTS
THE LARGEST OBSERVED
SOLAR COSMIC RAY EVENTS
LARGEST GLE
4580 % (15-min data)
Flare at 23 N, 80W
2nd LARGEST GLE
2150 % (5-min data)
Flare at 14 N, 61 W
4th LARGEST GLE
373 % (5-min data)
Flare at 105 W